UCLA quarterback Josh Rosen and USC quarterback Sam Darnold are among the preseason Heisman Trophy candidates and could be among the top 10 picks in the NFL Draft next spring. (Getty Images/Associated Press)

If they weren’t already rivals by design and definition, they would be rivals by default.

That’s just how it works with USC and UCLA, schools that share a city but fight over pretty much everything else.

Beginning this weekend, however, the chasm – one traditionally large and hollow enough to hold an echo – could be on the verge of widening to historic if not apocalyptic proportions.

That’s because the potential divide is being driven by two figures who could not be of more profound significance:

The schools’ starting quarterbacks.

Sam Darnold and Josh Rosen are about to open a competition during which they very well could battle for Pac-12 supremacy, for Heisman Trophy votes and, in eight months, for the distinction of being the No. 1 pick in the NFL draft.

Other than that, locally speaking, it’s just another average college football season, a cliched collection of student-athletes giving it 110 percent one game at a time.

Yeah, I know, this is the most team of all sports and, as such, Darnold and Rosen are dependent on all the other X’s being in the right places and all the other O’s executing the right moves.

Both also will require good fortune and good health, something Rosen had pounded out of him last fall by the end of his sixth game.

They, too, will need to avoid the seismic shifts that can rock a football season, Darnold’s ascension nationally in 2016 coming only after he first ascended from being a second-stringer on his own team.

But, like few previous years around here, this one could feature elite, NFL-prepping quarterback play at both USC and UCLA, simultaneous brilliance that culminates in much more than what happens when the Bruins visit the Coliseum on Nov. 18.

The possibilities are tantalizing, particularly given that in some other prominent programs today – like Michigan, for example – the starting quarterback has yet to be even publicly identified.

Everyone knows who’s starting for the Trojans and Bruins. Likewise, the expectations for each aren’t a secret, Darnold this month decorating the same regional Sports Illustrated cover that Rosen starred on last year.

The Darnold cover proclaimed him to be the Heisman Trophy leader entering the season, just as the Rosen cover predicted his performance and personality would hijack our attention.

Though the Bruins’ 2016 season fell apart after Rosen injured his shoulder, he hasn’t stopped making headlines despite the fact he largely has ceased engaging in social media and being made available to reporters.

Rosen’s next big public comment could come when UCLA plays Texas A&M at the Rose Bowl on Sunday, a day after Darnold begins attempting to fulfill SI’s projection against Western Michigan at the Coliseum.

In his most recent game, Darnold passed for 453 yards, five touchdowns and a Rose Bowl triumph so epic he should have received Heisman consideration retroactively, the award having been presented three weeks earlier.

As of mid-August, Darnold was listed as the 9/2 Heisman Trophy favorite by the Westgate SuperBook in Las Vegas. Rosen was the ninth choice at odds of 20/1.

Not since 2005 have the quarterbacks at USC (Matt Leinart, third) and UCLA (Drew Olson, eighth) finished together in the top 10 in Heisman voting.

That was the year Reggie Bush famously won the award in a landslide, only to later infamously lose the award. So, it is understandable if you’d forgotten what happened behind Bush in the final voting.

Before that, it was 1988, when USC’s Rodney Peete and UCLA’s Troy Aikman finished second and third, respectively, well behind Heisman winner Barry Sanders.

So this would not be a minor development, Darnold and Rosen trying to do something that has occurred rarely over the decades of shared football history between these programs.

Jeff Miller has been a sports columnist since 1998, having previously written for the Palm Beach Post, South Florida Sun-Sentinel and Miami Herald. He began at the Register in 1995 as beat writer for the Angels.

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